Yongfei Zeng

Covalent Organic Frameworks for CO2 Capture

As an emerging class of porous crystalline materials, covalent organic frameworks (COFs) are excellent candidates for various applications. In particular, they can serve as ideal platforms for capturing CO2 to mitigate the dilemma caused by the greenhouse effect. Recent research achievements using COFs for CO2 capture are highlighted. A background overview is provided, consisting of a brief statement on the current CO2 issue, a summary of representative materials utilized for CO2 capture, and an introduction to COFs. Research progresses on: i) experimental CO2 capture using different COFs synthesized based on different covalent bond formations, and ii) computational simulation results of such porous materials on CO2 capture are summarized. Based on these experimental and theoretical studies, careful analyses and discussions in terms of the COF stability, low- and high-pressure CO2 uptake, CO2 selectivity, breakthrough performance, and CO2 capture conditions are provided. Finally, a perspective and conclusion section of COFs for CO2 capture is presented. Recent advancements in the field are highlighted and the strategies and principals involved are discussed.

Engineering a Hollow Nanocontainer Platform with Multifunctional Molecular Machines for Tumor-Targeted Therapy in Vitro and in Vivo

In order to selectively target malignant cells and eliminate severe side effects of conventional chemotherapy, biocompatible and redox-responsive hollow nanocontainers with tumor specificity were fabricated. The mechanized nanocontainers were achieved by anchoring mechanically interlocked molecules, i.e., [2]rotaxanes, onto the orifices of hollow mesoporous silica nanoparticles via disulfide bonds as intermediate linkers for intracellular glutathione-triggered drug release. The [2]rotaxane employed was mainly composed of U.S. Food and Drug Administration approved tetraethylene glycol chains, α-cyclodextrin, and folic acid. In this study, folate groups on the mechanized hollow nanocontainers act as both the tumor-targeting agents and stoppers of the [2]rotaxanes. Detailed investigations showed that anticancer drug doxorubicin loaded mechanized nanocontainers could selectively induce the apoptosis and death of tumor cells. The drug-loaded nanocontainers enhanced the targeting capability to tumor tissues in vitro and inhibited the tumor growth with minimal side effects in vivo. The present controlled and targeted drug delivery system paves the way for developing the next generation of nanotherapeutics toward efficient cancer treatment.

Graphene-Based Microbots for Toxic Heavy Metal Removal and Recovery from Water

Heavy metal contamination in water is a serious risk to the public health and other life forms on earth. Current research in nanotechnology is developing new nanosystems and nanomaterials for the fast and efficient removal of pollutants and heavy metals from water. Here, we report graphene oxide-based microbots (GOx-microbots) as active self-propelled systems for the capture, transfer, and removal of a heavy metal (i.e., lead) and its subsequent recovery for recycling purposes. Microbots’ structure consists of nanosized multilayers of graphene oxide, nickel, and platinum, providing different functionalities. The outer layer of graphene oxide captures lead on the surface, and the inner layer of platinum functions as the engine decomposing hydrogen peroxide fuel for self-propulsion, while the middle layer of nickel enables external magnetic control of the microbots. Mobile GOx-microbots remove lead 10 times more efficiently than nonmotile GOx-microbots, cleaning water from 1000 ppb down to below 50 ppb in 60 min. Furthermore, after chemical detachment of lead from the surface of GOx-microbots, the microbots can be reused. Finally, we demonstrate the magnetic control of the GOx-microbots inside a microfluidic system as a proof-of-concept for automatic microbots-based system to remove and recover heavy metals.

Covalent Organic Frameworks Formed with Two Types of Covalent Bonds Based on Orthogonal Reactions

Covalent organic frameworks (COFs) are excellent candidates for various applications. So far, successful methods for the constructions of COFs have been limited to a few condensation reactions based on only one type of covalent bond formation. Thus, the exploration of a new judicious synthetic strategy is a crucial and emergent task for the development of this promising class of porous materials. Here, we report a new orthogonal reaction strategy to construct COFs by reversible formations of two types of covalent bonds. The obtained COFs consisting of multiple components show high surface area and high H2 adsorption capacity. The strategy is a general protocol applicable to construct not only binary COFs but also more complicated systems in which employing regular synthetic methods did not work.

Synergistic Effect of Mesoporous Co3O4 Nanowires Confined by N‐Doped Graphene Aerogel for Enhanced Lithium Storage

A one-step multipurpose strategy is developed to realize a sophisticated design that simultaneously integrates three desirable components of nitrogen dopant, 3D graphene, and 1D mesoporous metal oxide nanowires into one hybrid material. This facile synthetic strategy includes a one-step hydrothermal reaction followed by topotactic calcination. The utilization of urea as the starting reagent enables the precipitation of precursor nanowires and concurrent doping of nitrogen heteroatoms on graphene during hydrothermal reaction, while at the same time the graphene nanosheets are self-assembled to afford a 3D scaffold. Detailed characterizations on the final calcined product are conducted to confirm the phase purity, porosity, nitrogen composition, and morphology. The integration of two building blocks, i.e., flexible graphene nanosheets and Co3 O4 nanowires, enables various intertwining behaviors such as seaming, bridging, hooping, bundling, and sandwiching, of which synergistic effect substantially enhances electrical and electrochemical properties of the resultant hybrid. For lithium ion battery application of the hybrid, a remarkably high capacity more than 1200 mA h g(-1) (at 100 mA g(-1) ) is stabilized over 100 cycles with coulombic efficiency higher than 97%. Even during rapid discharge/charge processes (1000 mA g(-1) ), a reversible charge capacity of 812 mA h g(-1) is still retained after 230 cycles.

Bimetallic Metal-Organic Frameworks: Probing the Lewis Acid Site for CO2 Conversion.

A highly porous metal-organic framework (MOF) incorporating two kinds of second building units (SBUs), i.e., dimeric paddlewheel (Zn2 (COO)4 ) and tetrameric (Zn4 (O)(CO2 )6 ), is successfully assembled by the reaction of a tricarboxylate ligand with Zn(II) ion. Subsequently, single-crystal-to-single-crystal metal cation exchange using the constructed MOF is investigated, and the results show that Cu(II) and Co(II) ions can selectively be introduced into the MOF without compromising the crystallinity of the pristine framework. This metal cation-exchangeable MOF provides a useful platform for studying the metal effect on both gas adsorption and catalytic activity of the resulted MOFs. While the gas adsorption experiments reveal that Cu(II) and Co(II) exchanged samples exhibit comparable CO2 adsorption capability to the pristine Zn(II) -based MOF under the same conditions, catalytic investigations for the cycloaddition reaction of CO2 with epoxides into related carbonates demonstrate that Zn(II) -based MOF affords the highest catalytic activity as compared with Cu(II) and Co(II) exchanged ones. Molecular dynamic simulations are carried out to further confirm the catalytic performance of these constructed MOFs on chemical fixation of CO2 to carbonates. This research sheds light on how metal exchange can influence intrinsic properties of MOFs.

Surface Conductive Graphene-Wrapped Micromotors Exhibiting Enhanced Motion

Surface-conductive Janus spherical motors are fabricated by wrapping silica particles with reduced graphene oxide capped with a thin Pt layer. These motors exhibit a 100% enhanced velocity as compared to standard SiO2 -Pt motors. Furthermore, the versatility of graphene may open up possibilities for a diverse range of applications from active drug delivery systems to water remediation.

Reconstruction of Covalent Organic Frameworks by Dynamic Equilibrium.

Covalent organic frameworks (COFs) are periodic two- or three-dimensional polymeric networks with high surface areas, low density, and designed structures. Because COFs are normally prepared based on reversible formation of covalent bonds with relatively weak stability, their structures can be easily broken or damaged due to changes in the surrounding environment. Thus, developing strategies to realize the reconstruction of COFs in order to extend their usage lifetime is crucial for practical applications. In addition, exploring the kinetics of COF growth under varied reaction conditions is important for better understanding the nucleation and growth processes of COFs. In this work, the reformation mechanism of an imine-based COF using an ex situ characterization method was investigated, disclosing an interesting COF reconstruction progress from disorder to order. The present study shows the regeneration ability of COFs, and the developed method could be generalized for broader use in the field.

Iron(III)‐Quantity‐Dependent Aggregation–Dispersion Conversion of Functionalized Gold Nanoparticles

Developing gold nanoparticles (AuNPs) with well-designed functionality is highly desirable for boosting the performance and versatility of inorganic-organic hybrid materials. In an attempt to achieve ion recognition with specific signal expressions, we present here 4-piperazinyl-1,8-naphthalimide-functionalized AuNPs for the realization of quantitative recognition of Fe(III) ions with dual (colorimetric and fluorescent) output. The research takes advantage of 1) quantity-controlled chelation-mode transformation of the piperazinyl moiety on the AuNPs towards Fe(III), thereby resulting in an aggregation-dispersion conversion of the AuNPs in solution, and 2) photoinduced electron transfer of a naphthaimide fluorophore on the AuNPs, thus leading to reversible absorption and emission changes. The functional AuNPs are also responsive to pH variations. This strategy for realizing the aggregation-dispersion conversion of AuNPs with returnable signal output might exhibit application potential for advanced nanoscale chemosensors.

Metal-Organic Frameworks: Bimetallic Metal-Organic Frameworks: Probing the Lewis Acid Site for CO2 Conversion (Small 17/2016).

On page 2334, R. Q. Zou, Y. L. Zhao, and co-workers present a porous metal-organic framework (MOF) that serves as a platform for studying the metal exchange effect on both CO2 adsorption and catalytic fixation. The effect is demonstrated by catalytic CO2 cycloaddition with propylene oxide to produce propylene carbonate. Molecular dynamic simulations are carried out to further confirm the catalytic performance of these MOFs on chemical fixation of CO2 to carbonates. This research sheds light on how metal exchange could influence the intrinsic properties of MOFs.